Crime scene or nature reserve?

Forensic technique can be used for biological field studies

A method used by forensic experts to collect evidence from crime scenes could soon be taken up by biologists studying animals in the wild. An article in BMC Ecology this week describes how DNA from animal blood and tissue samples can be stored on record cards made from specialist filter paper and used in experiments at a later date.

“Techniques involving the analysis of DNA have become ubiquitous in many areas of wildlife research,” write Lee Smith and Leigh Burgoyne, who carried out the study. “Unfortunately the transport of fresh samples from the point of collection involves leakage risks and the possibility of sample degradation due to temperature variation.”

To avoid these problems the Australian researchers suggest collecting DNA samples on squares of specialist filter paper, called FTA® databasing paper, produced by Whatman. This paper is impregnated with a mix of chemicals that lyse cells, prevent bacterial growth and protect DNA from degradation.

The scientists outline methods that can be used to collect DNA from a variety of samples, including blood, blood clots, tissue extracts and cheek swabs. They go on to detail how these samples can be processed, taking account of several problems associated with samples of wildlife origin.

The basic premise is simple: Biological samples are applied to FTA® paper and air-dried. A small disc is then removed from the card, and washed to remove everything except the DNA, which remains entangled with the fibres of the paper. Analyses of the genetic material can be performed while it is still attached to the disc. Alternatively, the DNA can be washed off the disc with solvents before it is used in experiments.

Smith explains one of the many benefits of using this technique: “You can extract usable DNA from very small quantities of blood. Five micro-litres are more than enough for between five and ten analyses which makes live sampling much less invasive.”

To test the stability of the DNA samples, the researchers filed cards containing samples of bird blood in a box that they kept in a laboratory cupboard. Four years later, they successfully amplified DNA from these cards, demonstrating that, even though the temperature fluctuated between 18 degrees and 42 degrees centigrade, this treatment did not cause the samples to degrade significantly.

The researchers suggest that DNA on these cards can be transported cheaply, by mail or in hand luggage, whereas ’fresh’ samples would require refrigeration and dedicated transport systems. They comment: “The ease of transport and storage of samples dried on paper makes it practical for researchers to acquire large reference collections throughout their careers, just as they acquire large collections of printed references.” “I have between 500 and 100 samples stored in a card file on my desk,” said Smith.